The present invention relates to improving adhesion of polymeric materials to substrates, particularly curable compositions and film-forming compositions. Although not limited thereto, utility is particularly contemplated in the fields of adhesives and coatings.
Spot welding has been used in the past for structural support in doors, deck lids and hoods of automobiles; however, these weld points are sources of corrosion as well as cosmetic blemishes when done on exterior panels. Moreover, two-sided galvanized metals which are more frequently utilized do not readily lend themselves to spot welding. As a result, there has been a movement away from spot welding and toward use of structural adhesives either instead of or in conjunction with spot welding.
High strength structural adhesives are typically epoxy based compositions, and although they have good structural integrity, many are characterized by certain disadvantages, including non-uniform adhesion, variable corrosion resistance, lengthy cure times, poor adhesion to oily metal, high cost and toxicity problems.
Rubber-based vulcanizable compositions are also known in the art and have been typified by excellent strength and elongation. While these formulations offer good cure properties and weathering resistance, their utility has been limited by inconsistent adhesion to a variety of oily metals. Improving adhesion of rubber-based vulcanizable compositions to metals has been difficult, and adequate adhesion to substrates such as aluminum is rarely achieved. Rubber-based vulcanizable compositions with high sulfur loadings capable of further enhancing the strength and hardness of the rubber also suffer from poor or selective adhesion.
Adhesion promoters are also useful for coating compositions. Improving adhesion of organic, film-forming compositions to metal substrates is frequently sought after.